Generally, a broadband wireless access system supports an idle mode to minimize the power consumption of a mobile subscriber station (hereinafter abbreviated MSS).
A paging zone is defined as an entire zone that is taken charge of by a plurality of base stations included in one paging group. Each of the base stations included in the same paging zone has the same paging cycle Paging_Cycle and the same paging offset Paging_Offset.
The MSS can request a transition to an idle mode to the base station. The base station then delivers its paging group ID (Paging_group ID), a corresponding paging cycle and a corresponding paging offset. Thus, the corresponding MSS enter the idle mode.
During an idle mode, the MSS is capable of deciding whether to keep or terminate the idle mode via the paging delivered in the broadcast form from the base station each paging cycle.
If there occurs a traffic that has to be transmitted by an MSS in an idle mode, the MSS can terminate the idle mode at any time. If there occurs a traffic that has to be transmitted to an MSS in an idle mode, a base station is capable of enabling the MSS to terminate the idle mode via paging. Moreover, if an MSS, which has moved to another paging zone or has lost its sync, in an idle mode is unable to receive a paging at a predefined time, the MSS terminates the idle mode.
During the idle mode, the MSS needs not to perform a handover procedure in moving between base stations belonging to the same paging zone. Hence, the MSS needs not to transmit uplink information for the handover procedure to the base station, thereby reducing the corresponding power consumption. Namely, the MSS in the idle mode normally receives a periodic paging to secure its free move in the same paging zone without performing the handover procedure while there is no information to transmit/receive.
An idle mode transition process of an MSS according to a related art is explained in detail as follows.
First of all, an MSS transmits an idle mode request message to a serving base station to enter an idle mode. The serving base station then transmits a paging group ID, a paging cycle and a paging offset to the MSS via an idle mode response message and releases connection information to the MSS, radio resources allocated to the MSS and the like.
Table 1 shows an example of a format of an idle mode response message transmitted from a base station to an MSS requesting a transition to an idle mode, in which a conventional de-registration command message (DREG-CMD) is used.
TABLE 1SyntaxSizeNotesDREG-CMD_Message_Format( ) {Management Message Type = 298 bitsAction code8 bitsTLV encoded parametersVariable}
Table 2 and Table 3 shows examples of an action code definition of the de-registration command message and a format of TLV encoding, respectively.
TABLE 2ActionCodeAction0x00MSS shall leave the current channel andattempt to access another channel0x01MSS shall listen to the current channelbut shall not transmit until an RES_CMDmessage or DREG_CMD with Action Code isreceived.0x02MSS shall listen to the current channelbut shall only transmit on the Basic,Primary Management, and SecondaryManagement Connections.0x03MSS shall return to normal operations andmay transmit on any of its activeconnections.0x04MSS shall terminate current NormalOperations with the BS, the BS shalltransmit this action code only in responseto any MSS DREG_REQ.0x05Require MSS de-registration from ServingBS and request initiation of MSS idlemode.0x06The MSS may retransmit the DREG_REQmessage after the time duration (REQ-duration) given by.0x07The MSS shall not retransmit the DREG_REQmessage and shall wait for the DREG-CMDmessage.0x08-Reserved0xFF
TABLE 3NameTypeLengthValuePaging4Bits 15:0 -PAGING_CYCLEInformationBits 23:16 - PAGING OFFSETBits 31:24 - Paging Group IDREQ -1Standby value for retransmissionDurationof DREG-REQ message
If an action code of the de-registration command is set to 0x05 corresponding to an idle mode approval, the paging information shown in Table 3 is included in the de-registration command message to be transmitted to the MSS.
The base station notifies a MAC address of the MSS entering the idle mode to other base stations of the paging group to which the corresponding base station belongs. Hence, the corresponding base station enables the latter base stations to page the corresponding MSS with the same paging cycle and the same paging offset.
Via a broadcast-formatted paging message transmitted from the base station according to the paging cycle, the MSS allowed to enter the idle mode by the base station via the idle mode response message decides whether there exists a downlink traffic transmitted to the MSS itself exists, whether to perform a ranging, or whether to keep maintaining the idle mode.
Once confirming that there exists the downlink traffic via the paging message, the MSS terminates the idle mode and re-registers to a network to receive downlink data. If the MSS is requested to perform the ranging via the paging message, the MSS performs the ranging so that the base station can update a location of the MSS and a valid idle-mode MSS list. In case of failing in receiving a prescribed operation request via the paging message, the MSS keeps maintaining the idle mode.
If the MSS moves away into another base station of a different paging group or if the MSS terminates the idle mode due to the uplink or downlink traffic occurrence, the previous base station to which the MSS has belonged to notifies such a fact to the rest of the base stations of the previous paging group so that the corresponding MSS can be deleted from the idle mode list.
Table 4 shows an example of a data format of a broadcast-formatted paging message received by an MSS in idle mode from base stations of one paging group with a uniform cycle according to a related art.
TABLE 4SyntaxSizeNotesMOB_PAG-ADV_Message_Format( ) {Management Message8Type=??bitsNum_Paging Group IDs8Number of Paging GroupbitsIDs in this messageFor(i=0;i<Num_Paging_Group_IDs;i++) {Paging Group ID8bits}For(j=0; j<Num _MACs;Number of MSS MACj++) {Addresses in messagecan be determined fromthe length of themessage (found in thegeneric MAC header).MSS MAC address hash24The hash is obtained bybitscomputing a CRC24 onthe MSS 48-bit MACaddress. The polynomialfor the calculation is0x864CFB.Action Code2Paging actionbitsinstruction to MSS00 = No Action Required01 = Perform Ranging toestablish location andacknowledge message10 = Enter Network11 = ReservedReserved6bits}}
The paging message includes a paging group ID indicating a logical belonging of the transmitting base station, the MSS is identified by an MSS MAC address hash, and one paging message includes at least one or more MAC addresses. Moreover, the paging message transmits an action code to each MSS identified by corresponding MSS MAC address hash. The action code instructs a next action of the MSS in idle mode.
However, the related art method of allocating the paging information to the MSS in idle mode has the following problems.
First of all, the MSS, which enters the idle mode in the base station standing on a boundary between paging groups, may need considerable power consumption, which is explained in detail as follows.
The base station standing on the boundary between paging groups can have at least two paging group IDs to enable a flexible network design, thereby having at least two paging cycles and paging offsets. Namely, The base station standing on the boundary between paging groups can belong to at least two paging groups.
In case of receiving an idle mode request from an MSS, the base station belonging to the at least two paging groups allocates a random paging group ID among paging group IDs, to which the base station belongs, a corresponding paging cycle and a corresponding paging offset to transmit to the MSS via an idle mode response message. Yet, Since the MSS having entered the idle mode via the base station standing on the boundary between paging groups may exist on the boundary between the paging groups, it is highly probable that the MSS will move away into a different paging group from the allocated paging group in a short time.
If the idle-mode MSS having a specific paging group allocated thereto moves to a base station belonging to the different paging group, a paging cycle is changed. Hence, the corresponding MSS may not receive the paging message transmitted from the previously allocated paging group. And, the corresponding MSS should terminate the idle mode and should enter a normal operation mode.
Namely, it is highly probable that the MSS having entered the idle mode via the base station standing on the boundary between the paging groups terminates the idle mode quickly to enter the normal operation mode. And, the MSS needs to transmit/receive uplink/downlink message to enter the idle mode via the base station belonging to the new paging group, thereby increasing its power consumption.
Secondly, since a base station is unable to change an initial paging cycle and offset, which are initially allocated when an MSS enters an idle mode, as long as the MSS maintains the idle mode, it is difficult to adjust a paging load of the base station.
Thirdly, in case that a base station having at least two paging group IDs allocates paging information to an MSS, there is no concrete reference for what kind of paging group information shall be allocated to the MSS. Namely, if one paging information of the at least two paging groups is allocated, the paging information is allocated by selecting the paging group randomly without considering a paging load of the paging group.